Conventional wind turbines are typically supported by a relatively complex and expensive support tower for placing wind turbine blades at high positions relative to the ground and for accommodating reaction loads due to freestream wind forces over the wind-turbine blades. And, conventional wind turbines can operate at relatively high rotational speeds which requires precision fabrication, balancing and complex support and controlling structures.
Furthermore, power is also conventionally obtained from the wind turbine at the top of the support tower. This requires the support tower to additionally accommodate the weight of the power take-off means, such as a generator, and makes maintenance difficult.
One type of conventional wind turbine includes vertically oriented blades mounted to a hub which rotates in a plane parallel to the ground. In such an arrangement, the rotating hub has a leeward side wherein the blades move away from the wind and the freestream airflow pushes, or lifts, the wind turbine blades and is in the same direction therewith. The hub also has a windward side wherein the blades are moving toward or against the wind in a direction opposition to the direction of the freestream wind. In order for such a wind turbine to operate, the pitch of the blade, which is the angular position of the blade relative to the freestream airflow, must be continuously changed for providing lift on the leeward side of the hub and minimum drag on the windward side of the hub.
Conventional wind turbines include a central control vane responsive to freestream wind direction which is disposed generally parallel thereto and operatively connected to the blades for continuously changing the pitch thereof as the blades rotate with the hub about a central axis. However, a central control vane senses freestream airflow direction and does not account for either the relative, or apparent, wind direction experienced by each of the rotating blades, or any turbulence which may be acting upon any of the blades in operation.